<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <div id="app">
    <div>{{name}}</div>
  </div>
  <script src='../dist/vue.js'></script>
  <script>
    const vm = new Vue({
      data() {
        return {
          name: 'allen'
        }
      },
      watch: {
        name(newVal, oldVal) {
          console.log('name ', newVal, oldVal)
        }
      },
      el: '#app'
    })
    setTimeout(() => {
      vm.name = 'tom'
    }, 1000)
  </script>
</body>

</html>